Antisense technology is an effective means for reducing the expression of one or more specific gene products and can therefore prove to be uniquely useful in a number of therapeutic, diagnostic, and research applications. Chemically modified nucleosides are routinely used for incorporation into antisense sequences to enhance one or more properties such as for example nuclease resistance. One such group of chemical modifications includes bicyclic nucleosides wherein the furanose portion of the nucleoside includes a bridge connecting two atoms on the furanose ring thereby forming a bicyclic ring system. Such bicyclic nucleosides have various names including BNA's and LNA's for bicyclic nucleic acids or locked nucleic acids respectively.
Various BNA's have been prepared and reported in the patent literature as well as in scientific literature, see for example: Singh et al., Chem. Commun., 1998, 4, 455-456; Koshkin et al., Tetrahedron, 1998, 54, 3607-3630; Wahlestedt et al., Proc. Natl. Acad. Sci. U.S.A., 2000, 97, 5633-5638; Kumar et al., Bioorg. Med. Chem. Lett., 1998, 8, 2219-2222; Wengel et al., PCT International Application WO 98-DK393 19980914; Singh et al., J. Org. Chem., 1998, 63, 10035-10039, the text of each is incorporated by reference herein, in their entirety. Examples of issued US patents and published applications include for example: U.S. Pat. Nos. 7,053,207, 6,770,748, 6,268,490 and 6,794,499 and published U.S. applications 20040219565, 20040014959, 20030207841, 20040192918, 20030224377, 20040143114 and 20030082807; the text of each is incorporated by reference herein, in their entirety.
Many LNA's are toxic. See, e.g., Swayze, E. E.; Siwkowski, A. M.; Wancewicz, E. V.; Migawa, M. T.; Wyrzykiewicz, T. K.; Hung, G.; Monia, B. P.; Bennett, C. F., Antisense oligonucleotides containing locked nucleic acid improve potency but cause significant hepatotoxicity in animals. Nucl. Acids Res., doi: 10.1093/nar/gkl1071 (December 2006, advanced online publication).
One carbocyclic BNA has been previously reported (Frier et al., Nucleic Acids Research, 1997, 25 (22), 4429-4443) having a 4′-(CH2)3-2′ bridge. This modification was reported to drop the Tm about 2.5° C. per modification for a poly T oligomer having a BNA T nucleoside in place of one or more T nucleosides when hybridized to complementary RNA. This same BNA having the 4′-(CH2)3-2′ bridge as reported by Frier et al., or the alkenyl analog bridge 4′-CH═CH—CH2-2′ has also been reported to have increased stability with an increased Tm of from about 2.5 to 5.0° C. per modification (see Albaek et al., J. Org. Chem., 2006, 71, 7731-7740).
Carbocyclic bicyclic nucleosides and oligonucleotides prepared therefrom have been recently reported by Srivastava et al., J. Am. Chem. Soc. 2007, 129(26), 8362-8379, published on line on Jun. 7, 2007.
There remains a long-felt need for agents that specifically regulate gene expression via antisense mechanisms. Disclosed herein are carbocyclic BNA's and antisense compounds prepared therefrom useful for modulating gene expression pathways, including those relying on mechanisms of action such as RNaseH, RNAi and dsRNA enzymes, as well as other antisense mechanisms based on target degradation or target occupancy. One having skill in the art, once armed with this disclosure will be able, without undue experimentation, to identify, prepare and exploit antisense compounds for these uses.